1. Field of the Application
The present invention relates to apparatus for melting metals, and more particularly to a channel-type induction furnace.
The invention is applicable for use in manufacturing channel-type induction furnaces provided with a plurality of induction coils and intended for holding liquid metals and melting solid metals and alloys.
2. Description of the Prior Art
There is known a channel-type induction furnace which comprises a hearth and the so-called induction unit which may include one or more transformer cores mounting induction coils with channels being disposed therebetween and communicating with the hearth, said channels communicating with one another through a horizontal channel and containing a molten metal.
The above-mentioned melting channels form loops which embrace the induction coils. With the induction coils being connected to an a.c. power source, the electric current passes through the channels to result in the heat energy generated in the molten metals contained in said channels. The released heat is then transferred to the molten metal contained in the furnace hearth.
The best operating conditions of the furnace are such that provide for great velocity of molten metal flow through the channels. This makes it possible to effectively transfer the heat generated in the channels to the metal found in the hearth, permits the temperature of the molten metal found in the channels to be decreased, and, finally, enables the provision of channel-type induction furnaces having high operative capacity and long service life of the refractory lining.
U.S. Pat. No. 2,539,800 discloses a channel-type induction furnace which comprises two induction coils and three intercommunicating channels connected with one another through a horizontal channel (the so-called twin coil induction unit). In order to provide for unidirectional flow of metal to the inlet opening of the central channel, a tubular member of electrically conductive refractory material is mounted so as to intimately adjoin the inlet opening of said channel.
Owing to the use of electrically conductive material, the electric current passing through the channel follows the same path with or without the presence of the tubular member, whereas the metal is caused to move by reason of "electromagnetic pumping" or "pinch effect" along the path extending through the hearth, lateral channels, horizontal channels, central channel and back to the hearth again. The furnace construction in question have not found wide application because of the low velocity of metal flow.
U.S. Pat. No. 3,595,979 describes a channel-type induction furnace construction now in wide use wherein a unidirectional flow of liquid metal passes through the channels of the twin coil induction unit. The unidirectional flow of metal in this furnace construction is ensured due to a special shape given to the inlet opening of the central channel. Let us consider this at greater length. The distribution of the electric current passing through the twin induction units results in the appearance of eddies or turbulence in the inlet openings of the lateral and central channels. These eddies cause the metal to eject from the channels. Since the eddies act with different intensity in the central channel and in the lateral channels, the melt is pumped through said channels. With the inlet end of the central channel outflaring in two directions, turbulence becomes more vigorous in this area, thus allowing for a unidirectional flow of metal. However, due to stagnation in the movement of metal inside of the melting channels, i.e. the metal moves in a counter-current flow to the unidirectional flow of metal at certain places of the inlet opening of the channel, the velocity of the metal unidirectional flow is reduced under the effect of turbulence at the inlet openings of the lateral channels.
In the course of the furnace operation the inlet openings of the channels change their shape, increasing or decreasing in cross section under the action of molten metal, whereby the velocity of molten metal flow is reduced in the known furnace construction. This, in turn, causes the overheating of metal contained in the channel and leads to premature failure of the induction unit.